Light absorptive antireflector

ABSTRACT

A light absorptive antireflector comprising a substrate, a light absorbing film formed on the substrate and a silica film formed on the light absorbing film, to reduce reflection of incident light from the silica film side, wherein the geometrical film thickness of the light absorbing film is from 5 to 25 nm, and the geometrical film thickness of the silica film is from 70 to 110 nm.

This is a Division of application Ser. No. 08/571,299 filed on Dec. 12,1995, now U.S. Pat. No. 5,691,044.

TECHNICAL FIELD

The present invention relates to a light absorptive antireflector.

BACKGROUND ART

In recent years, along with rapid expansion of computers, it has beendesired to reduce reflection on a display surface or to preventelectrification of the surface of CRT (cathode ray tubes) in order toimprove the working environment of the terminal operators. Further,recently, it has been demanded to reduce the transmittance of the panelglass in order to improve the contrast, or to shield electromagneticwaves of extremely low frequencies which may adversely affect humanbodies.

To respond to such demands, methods have been adopted such that (1) anelectroconductive antireflection film is provided on the panel surface,(2) an electroconductive antireflection film is formed on the surface ofa face plate of CRT etc., which is then bonded to a panel surface by aresin, and (3) a filter glass having an electroconductive antireflectionfilm formed on each side is disposed in front of a cathode ray tube.

Among them, in the case of methods (2) and (3), it is common to form theantireflection film in a plurality of layers by a vacuum depositionmethod. A specific example of such a film construction may be the onedisclosed in Japanese Unexamined Patent Publication No. 168102/1985.This publication discloses that an antireflection film is formed by acombination of a dielectric film with a low refractive index, adielectric film with a high refractive index and an electroconductivefilm with a high refractive index. By coating a multilayerantireflection film having such a film construction on a panel surface,the visible reflectance of the surface can be reduced to 0.3% or less,and the surface resistance can be reduced to 1 kΩ/□ or less. Further,the above-mentioned electromagnetic wave-shielding effect can thereby beimparted.

Further, as a method of increasing the contrast, it has been known thatit is effective to use a light absorbing film as a part of itsconstruction. For example, Japanese Unexamined Patent Publication No.70701/1989 discloses a case wherein a stainless steel film having a filmthickness of 4 nm, a titanium oxide film having a film thickness of 29nm and a silica film having a film thickness of 95 nm were sequentiallyformed on a glass substrate by a vacuum vapor deposition method. Bycoating a multilayer absorptive antireflection film of this constructionon a panel surface, the visible reflectance of the surface can bereduced to 0.3% or less, and the surface resistance can be reduced to 1kΩ/□ or less. Further, at the same time, the visible light transmittancecan be reduced by a few tens %, whereby a high contrast can be attained.

On the other hand, method (1) include (a) a case wherein a panel iscoated first, and then formed into a cathode ray tube, and (b) a casewherein a cathode ray tube is first formed and then surface coating isapplied thereto. In either case, a so-called wet method such as spincoating is relied upon presently.

If a so-called dry method such as the above-mentioned vacuum vapordeposition method is used, in the case of (a), there is a problem suchthat due to the heat treatment in the step for forming a cathode raytube after film forming, the film properties will be changed, and thedesired performance can not be obtained. In the case of (b), it isnecessary to set the entire cathode ray tube in a vacuum chamber.Accordingly, there will be restrictions in the volume and weight, andthere is a problem that the handling is not easy.

A sputtering method as a typical film forming method of dry system hashad a difficulty in high speed stable film formation of SiO₂ which is alow refractive index material essential for the construction of anantireflection film. Therefore, in the sputtering method, no technologyhas been established for an industrial production of an antireflectionfilm with a large area.

However, recently, due to the increasing demand for high levels ofproperties as mentioned above, the following problems have been pointedout for the surface treatment by a wet method. Namely, (1) in a wetmethod, control of the film thickness is difficult as compared with adry method, and there is a difficulty in reproducibility or uniformity,when it comes to a multilayer film construction of at least threelayers, which is desired for good antireflection performance, (2) thelower limit of the surface resistance so far attained by the wet methodis about 10³ kΩ/□, which may be adequate for antistatic purposes, but itis difficult to attain 1 kΩ/□ which is required for shieldingelectromagnetic waves, and (3) it is difficult to impart absorptivitywithout impairing the antireflection performance.

On the other hand, the vapor deposition method has, in addition to theabove-mentioned problem in the heat stability of the film properties, aproblem that the film forming cost is substantially higher than the wetmethod, and it has been desired to develop an inexpensive film formingmethod.

Under these circumstances, various attempts have recently been made todevelop a method for forming SiO₂ stably at a high speed by sputtering.As a result, several methods are now being practically developed. Forexample, MMRS (metal mode reactive sputtering) as disclosed in U.S. Pat.No. 4,445,997 and C-Mag (cylindrical magnetron) as disclosed in U.S.Pat. No. 4,851,095 may be mentioned.

As a result, an antireflection film by sputtering is about to berealized. However, with respect to the construction of theantireflection film, the construction of a film which has heretoforebeen formed by vacuum vapor deposition is followed in many cases, and nofilm construction particularly effective by sputtering has been known.

The following constructions are known as conventional examples ofantireflection films.

For example, J. D. Rancourt "Optical Thin Films User's Handbook"(McGRAW-HILL 1987) discloses at page 128 a spectral reflection curve ina case where a light absorbing film with a complex refractive index(n-ik)=2-i2 and a transparent film with n=1.65 are formed in thicknessesof 3 nm and 75.8 nm, respectively, in this order on a substrate with arefractive index of 2.35. However, in this case, presented aretheoretical calculated values, and the reflection characteristics areexplained as those corresponding to a so-called "V coat", where thereflection becomes 0 only with a single wavelength shown by atransparent double layer film which is a basic construction forantireflection. Thus, they do not represent low reflectance in a widerange wavelength region (such as from 500 to 650 nm).

Further, U.S. Pat. No. 5,091,244 discloses a case where a transitionmetal nitride film and a transparent film are formed in film thicknessesof from 6 to 9 nm and from 2 to 15 nm, respectively, sequentially from asubstrate side, as a construction to reduce the reflection to incidentlight from the substrate side (i.e. incident light from the sideopposite to the film surface side).

When a light absorbing film having a proper optical constant is formedin a thin thickness, the reflectance from the substrate side decrease,as disclosed, for example, in "Thin-Film Optical Filters", H. A.Macleod, MaGraw-Hill Publishing Co., 2nd Ed., pp65-66 (1989).

In the U.S. Patent, SiO₂ is laminated in a thin thickness (from 2 to 15nm).

However, this construction is designed for the purpose of reducing thereflection from the substrate side. In the case of a multilayered filmcontaining a light absorbing film, the reflection is totally differentas between the front and rear sides. Therefore, with this constructioninvented for the purpose of reducing the reflection from the substrateside, the reflectance from the film surface side is about 10% over theentire visible light region, whereby no reflection-reducing effect isobtained.

U.S. Pat. No. 5,091,244 discloses a four layer construction ofglass/transition metal nitride/transparent film/transition metalnitride/transparent film, as a construction to reduce the reflection onthe film surface side. However, the object is to reduce the visiblelight transmittance to 50% or less, and this object is attained byadding an another light absorbing layer and making the number of layersat least four layers, whereby there has been a practical problem fromthe viewpoint of the production cost.

As described in the foregoing, a film construction has not been knownwherein a light absorbing film is contained as a constituting element,the film construction is basically a double layer construction, wherebythe production cost is low, and it provides low reflectance within awide range wavelength region to incident light from the film surfaceside.

DISCLOSURE OF INVENTION

It is an object of the present invention to solve the above-mentioneddrawbacks of the prior art and to provide a light absorptiveantireflector which simultaneously has a sufficiently low reflectionproperty within a wide range wavelength region, a sufficiently lowsurface resistance for shielding electromagnetic waves and a propervisible light absorption to secure a high contrast and which isinexpensive and excellent in the productivity.

The present invention provides a light absorptive antireflectorcomprising a substrate, a light absorbing film formed on the substrateand a silica film formed on the light absorbing film, to reducereflection of incident light from the silica film side, wherein thegeometrical film thickness of the light absorbing film is from 5 to 25nm, and the geometrical film thickness of the silica film is from 70 to110 nm (hereinafter referred to as the first aspect of the invention).

The present invention also provides a light absorptive antireflectorcomprising a substrate, a light absorbing film formed on the substrate,a transparent film having a high refractive index formed on the lightabsorbing film and a silica film formed on the transparent film, toreduce reflection of incident light from the silica film side, whereinthe geometrical film thickness of the light absorbing film is from 15 to30 nm, the geometrical film thickness of the transparent film having ahigh refractive index is from 10 to 40 nm, and the geometrical filmthickness of the silica film is from 50 to 90 nm (hereinafter referredto as the second aspect of the invention).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of one embodiment of thepresent invention.

FIG. 2 is a schematic cross-sectional view of another embodiment of thepresent invention.

FIG. 3 is a graph showing a change with time of the voltage applied to asilicon target, as used in Examples and Comparative Examples.

FIG. 4 is a graph showing the spectral reflectance and the spectraltransmittance of Example 1.

FIG. 5 is a graph showing the spectral reflectance and the spectraltransmittance of Example 16.

FIG. 6 is a graph showing the spectral reflectance of Example 3.

FIG. 7 is a graph showing the spectral reflectance of Example 8.

FIG. 8 is a graph showing the spectral reflectance of Example 9.

FIG. 9 is a graph showing the spectral reflectance and the spectraltransmittance of Example 17.

FIG. 10 is a graph showing the spectral reflectance of Example 4.

FIG. 11 is a graph showing the spectral reflectance of Example 5.

FIG. 12 is a graph showing the spectral reflectance of Example 14.

FIG. 13 is a graph showing the spectral reflectance of Example 15.

FIG. 14 is a graph showing the spectral reflectance after heat treatmentof Example 3.

FIG. 15 is a graph showing the spectral reflectance after heat treatmentof Example 7.

FIG. 16 is a graph showing a distribution relation of the opticalconstant of an ideal light absorbing film, as obtained by calculation.

FIG. 17 illustrates various embodiments in which the light absorptiveantireflector of the present invention is used.

In the first aspect of the invention, it is important that thegeometrical film thickness (hereinafter, "the geometrical filmthickness" will be referred to simply as "the film thickness") of thelight absorbing film is from 5 to 25 nm to attain the low reflection,and the film thickness of the silica film is from 70 to 110 nm also fromthe viewpoint of antireflection. If the film thickness of either layeris outside such a range, no adequate antireflection performance in thevisible light region tends to be obtained. Particularly preferred as thefilm thickness range of the light absorbing film is from 7 to 20 nm,whereby low reflectance can be attained over the entire visible lightregion. Further, preferred as the film thickness range of the silicafilm (having preferably a refractive index of 1.46-1.47) is form 80 to100 nm, whereby the low reflection wavelength range can be adjusted tothe center potion of the visible light region.

It is particularly preferable that the film thickness of the silica filmis more than 80 nm but not more than 85 nm. If the film thickness of thesilica film is not more than 80 nm, the reflectance on the longwavelength side tends to increase, and if the film thickness of thesilica film is more than 85 nm, the rising of the reflectance on theshort wavelength side tends to be shifted to the long wavelength side.

Further, from the viewpoint of the heat resistance, the film thicknessof the light absorbing film in the first aspect of the invention ispreferably from 10 to 20 nm. If the film thickness is less than 10 nm,deterioration of the low reflection performance or the surfaceresistance during the heat treatment tends to be substantial, and if thefilm thickness exceeds 20 nm, the antireflection region tends to benarrow, although the heat resistance will be improved.

On the other hand, from the viewpoint of the low reflection performanceafter film formation, the film thickness of the light absorbing film inthe first aspect of the invention is preferably from 7 to 15 nm. If thefilm thickness is less than 7 nm, the reflectance on the long wavelengthside tends to remarkably increase, and if the film thickness exceeds 15nm, the low reflection wavelength region tends to be narrow.

Also, the film thickness of the light absorbing film is more than 8 nmbut less than 13 nm, preferably more than 8 nm but not more than 10 nm.If the film thickness of the light absorbing film is not more than 8 nm,the reflectance on the long wavelength side tends to increase, and ifthe film thickness of the light absorbing film is not less than 13 nm,the rising of the reflectance on the short wavelength side tends to beshifted to the long wavelength side and the rising of the reflectance onthe long wavelength side tends to be shifted to the short wavelengthside, and accordingly the low reflection wavelength region tends to benarrow.

The light absorptive antireflector according to the first aspect of theinvention exhibits excellent antireflection characteristics, but in somecases, deterioration of the characteristics may be observed during theheat treatment step in the process for forming a cathode ray tube, asmentioned above. This change of the characteristics is caused mainly byoxidation of the light absorbing film.

Further, it may happen that after forming the light absorbing film asthe first layer, the light absorbing film undergoes oxidation at thetime of forming a silica film as the second layer, whereby the desiredcharacteristics can not be obtained.

In such a case, it is possible to prevent oxidation during the filmforming or to improve the heat resistance by inserting a layer toprevent oxidation of the light absorbing film (hereinafter referred toas an oxidation barrier layer) between the light absorbing film and thesilica film.

An oxidation barrier layer of this type is the one widely used inso-called Low-E glass wherein a silver film is used. For example, U.S.Pat. No. 4,548,691 and Japanese Unexamined Patent Publication No.165001/1984 teach to form a barrier layer for the purpose of preventingoxidation of a silver layer during the film formation of an oxide filmto be formed on the silver film. As such, this barrier layer is a thinfilm formed to prevent oxidation of another layer formed beneath, andaccordingly has no optical significance.

As such an oxidation barrier layer, various metal films or metal nitridefilms may be employed. The thickness is preferably at most 20 nm not toimpair the desired antireflection performance. If the thickness of thisoxidation barrier layer is less than 1 nm, improvement of the heatresistance tends to be inadequate. Accordingly, it is preferred toinsert an oxidation barrier layer having a thickness of from 1 to 20 nm,whereby the heat resistance can be improved effectively.

As mentioned above, the oxidation barrier layer has no opticalsignificance and is a layer unnecessary from the optical point of view.Accordingly, by the insertion of this layer, the antireflectionperformance may deteriorate in some cases. Especially in a case whereoxidation barrier layer is light absorptive (e.g. light absorptivesilicon nitride), the antireflection performance may substantiallydeteriorate unless the thickness of the oxidation barrier layer is madeat most about 5 nm.

When a transparent oxide barrier layer is employed, the allowable filmthickness varies depending upon the refractive index of this layer. Theallowable film thickness will be largest when a material having arefractive index of about 2.0 (such as transparent silicon nitride oraluminum nitride) is employed. It is possible to insert a barrier layerof up to about 20 nm between the lower nitride layer and the uppersilica layer, while maintaining the low reflection characteristics.

As the oxidation barrier layer, it is preferred to employ a filmconsisting essentially of at least one metal selected from the groupconsisting of chromium, molybdenum, tungsten, vanadium, niobium,tantalum, zinc, nickel, palladium, platinum, aluminum, indium, tin andsilicon, or a film consisting essentially of a nitride thereof, or afilm consisting essentially of at least one metal selected from thegroup consisting of titanium, zirconium and hafnium, whereby adequateimprovement of the antioxidation performance and maintenance ofexcellent antireflection characteristics can be simultaneously beattained.

Especially, a film consisting essentially of silicon or a filmconsisting essentially of a nitride of silicon is excellent in theoxidation barrier performance. Besides, when the silica film is formedby sputtering from an electroconductive Si target, the target materialis not required to be changed, which is advantageous from the viewpointof the production.

Against the visible light incident from the silica film side, the lightabsorption of the light absorptive antireflector according to the firstaspect of the invention is preferably from 10 to 35%. If the lightabsorption is outside this range, the film thickness range of the lightabsorbing film is improper, or the optical constant of the lightabsorbing film is improper, whereby no adequate antireflectionperformance in the visible light region tends to be obtained.

As the transparent film having a high refractive index in the secondaspect of the present invention, it is preferred to employ a materialhaving a refractive index of at least 1.7. If the refractive index issmaller than 1.7, no substantial improvement in the antireflectionperformance due to the insertion of the transparent film with a highrefractive index will be observed. As a specific material, Y₂ O₃, ZrO₂,ZnO, SnO₂, Ta₂ O₅ or TiO₂ may, for example, be used.

Further, a transparent conductive film such as ITO may also be used. Inthis case, the surface resistance will be determined by the parallelresistance of the light absorbing film layer and this transparentelectroconductive film layer, whereby reduction of the resistance may beeasy as compared with a case where electroconductivity is provided onlyby the light absorbing film such as titanium nitride.

It is important that the film thickness of the light absorbing film inthe second aspect of the invention is from 15 to 30 nm to attain the lowreflection, the film thickness of the transparent film having a highrefractive index is from 10 to 40 nm, and the film thickness of thesilica film is from 50 to 90 nm also from the viewpoint of theantireflection. If the film thickness of either one of these layers isoutside such a range, no adequate antireflection performance in thevisible light region tends to be obtained.

An oxidation barrier layer may also be provided in the light absorptiveantireflector according to the second aspect of the present invention.In the light absorptive antireflector according to the second aspect ofthe invention, an oxidation barrier layer having a thickness of from 1to 20 nm may be formed between the light absorbing film and thetransparent film having a high refractive index, or between thetransparent film having a high refractive index and the silica film.

As the oxidation barrier layer, the same material as preferably used inthe light absorptive antireflector according to the first aspect of theinvention, can be used preferably.

Against the visible light incident from the silica film side, the lightabsorption of the light absorptive antireflector according to the secondaspect of the invention is preferably from 30 to 60%. If the lightabsorption is outside this range, the film thickness range of the lightabsorbing film is improper, or the optical constant of the lightabsorbing film is improper, whereby no adequate antireflectionperformance in the visible light region tends to be obtained.

As the substrate in the first and second aspects of the invention, glassor plastics may be used. It is particularly preferred that the substrateis a glass substrate, a plastic substrate or a plastic film, whichconstitutes the front surface of a display screen, whereby the effectsof the present invention can adequately be obtained.

Glass as the substrate to be used for the front surface of a displaymay, for example, be a panel glass constituting a cathode ray tubeitself, a face plate glass to be used as attached to a cathode ray tubeby a resin, or a filter glass disposed between a cathode ray tube and anoperator. Further, a front glass of a flat display such as a liquidcrystal display panel or a plasma display panel, may also be mentioned.

A plastic as the substrate or film to be used for the front surface of adisplay may, for example, be 1) a transparent film-type plastic such asPET (polyethylene terephthalate) to be used as attached by a resin tothe front glass of a cathode ray tube or the above-mentioned flatdisplay, 2) a transparent plastic as a filter substrate disposed betweena cathode ray tube and an operator, or 3) a transparent plastic sheetconstituting the front surface of a flat display.

FIG. 17 illustrates various embodiments in which the light absorptiveantireflector of the present invention is used.

As shown in FIG. 17, the light absorptive antireflector of the presentinvention having the antireflection film formed on the substrate surfaceonly on the side of an observer has excellent antireflectioncharacteristics. Further, since the antireflection film is formeddirectly on the substrate surface generating electromagnetic radiations,the electromagnetic radiations can be quite effectively shielded.

Also, when the light absorptive antireflector is applied to the filterglass, it is preferable to form the antireflection film on the substratesurface also on the opposite side of an observer.

For the light absorbing film in the first and second aspects of theinvention, a material is used which is capable of substantially reducingthe surface reflectance by the light interference effect with the silicalayer formed thereon.

Such a light absorbing film say, for example, be the one consistingessentially of at least one metal selected from the group consisting oftitanium, zirconium and hafnium, or the one consisting essentially ofnitride of such metal. Among them, it is preferred to employ the oneconsisting essentially of a nitride of at least one metal selected fromthe group consisting of titanium, zirconium and hafnium, in view of thedispersion relation of the extinction coefficient and the refractiveindex in the visible light region, whereby there is a feature that thelow reflection region in the visible light range will be broadened bythe optical constants thereof.

When two or more materials are employed, 1) they may be used in the formof a composite material, or 2) they may be used in the form of alaminate of a plurality of layers of different materials in a totalthickness of from 5 to 25 nm.

Further, a film consisting essentially of a nitride of titanium isparticularly preferred, since its optical constants in the visible lightregion well matches with silica to reduce the reflectance and at thesame time the light absorption is proper, and the film thickness toobtain a proper light absorption is within a range of a few nm to a fewtens nm. Therefore, this film is particularly preferred from theviewpoint of both the productivity and the reproducibility.

In a case where as the light absorbing film, the one consistingessentially of a nitride of a metal is used, if a film consistingessentially of a nitride is used as the above-mentioned oxidationbarrier layer, the first layer and the barrier layer can be formed bysputtering in the same gas atmosphere. This is a substantial merit ifthe actual film forming apparatus by sputtering is taken into account.Namely, when a so-called in-line type sputtering apparatus which isexcellent in the mass productivity, is taken into account, such a lightabsorbing film and an oxidation barrier layer can be formed in the samechamber (chamber A). Therefore, a chamber for gas separation may beprovided only between chamber A and a chamber for forming the silicafilm to be formed thereon, such being extremely efficient.

Especially when a film consisting essentially of titanium nitride isused as the first layer, and silicon nitride is used as the oxidationbarrier layer, an additional effect will also be obtained such that theadhesion between the titanium nitride film and the silica film as theoutermost layer, is improved. In this case, if both films are formed byan in-line sputtering method in the same chamber, the silicon nitridefilm as the oxidation barrier layer becomes light absorptive under thesputtering gas condition where suitable titanium nitride is obtainable.Further, the effect for improving the adhesion is likewise obtainable.

As a means for forming the light absorbing film, the transparent filmhaving a high refractive index and the silica film in the first andsecond aspects of the invention, a common thin film-forming means may beemployed. For example, a sputtering method, a vacuum vapor depositionmethod, a CVD method or a sol-gel method may, for example, be mentioned.Especially, the DC sputtering method is preferred from the viewpointssuch that control of the film thickness is relatively easy, practicalfilm strength can be obtained even when the film is formed on a lowtemperature substrate, a film with a large area can easily be formed,and formation of a laminated film is easy if a so-called in-line typeinstallation is used. Another merit is that control of the film formingconditions is relatively easy so that the nitride of titanium, zirconiumor hafnium, which is preferred as the light absorbing film, will havepreferred optical constants.

Further, when an in-line type sputtering apparatus is employed, the filmthickness distribution in the width direction of transportation can beadjusted to some extent by e.g. the magnetic field intensitydistribution of the cathode magnet or by installation of a mask plate.Accordingly, in a case where a substrate is used as the front surface ofa display, the film thickness along the periphery of the substrate canbe set to be slightly thicker than the central portion. To provide sucha film thickness distribution on the substrate is practically preferred,since it is thereby possible to reduce a phenomenon that the reflectedcolor tends to drift to yellow or red by the effect of oblique incidenceof light when the periphery of the screen is viewed from the center.

The vacuum vapor deposition method has drawbacks that it is essential toheat the substrate, it is difficult to attain a large surface area, andit is relatively difficult to obtain a satisfactory nitride. However, inthe case of a substrate material which is relatively small in size anddurable at high temperatures, the vacuum vapor deposition method isadvantageous in that as a process, this method has been most completelyestablished.

The CVD method requires a still higher temperature, and it is difficultto attain a large surface area from the viewpoint of the film thicknessdistribution. However, this is an excellent method to obtain asatisfactory nitride.

The sol-gel method is a wet method as mentioned in the technicalbackground and has been used as a technique for the surface treatment ofa cathode ray tube. However, it is relatively difficult to obtain asatisfactory nitride, and the operation will be a batch treatment forevery film. However, the installation cost is small, and this method maybe advantageous from the viewpoint of the costs for the production of asmall quantity of products.

The light absorptive antireflection film of the present invention may beformed by a combination of these methods. For example, the lightabsorbing film of the first layer may be formed by a sputtering methodwhereby relatively preferred optical constants can be obtained, and thenthe transparent film having a high refractive index and/or the silicafilm may be formed by spin coating as a wet method excellent in the filmforming cost. Likewise, the light absorbing film of the first layer maybe formed by a CVD method, and then the transparent film having a highrefractive index and/or the silica film may be formed by spin coating asa wet method excellent in the film forming cost. In this case, the lightabsorbing film already formed as the first layer may sometimes becorroded depending upon the spin coating solution, whereby the desiredcharacteristics may not be obtained. For example, in a case where a spincoating liquid comprising 0.1N hydrochloric acid, tetraethoxysilane andethyl alcohol, is used, it is preferred to form an oxide film or anitride film having good durability as the protective film of the firstlayer, prior to the spin coating.

As described above, various methods and their combinations may be usedfor the formation of the light absorptive antireflection film of thepresent invention (the fist and second aspects of the invention).However, the present invention is not limited to such specific examples.

As a light absorbing film consisting essentially of a nitride oftitanium (hereinafter referred to as a TiN light absorbing film), it ismost preferred to employ the one formed by DC sputtering of a metaltitanium target in the presence of nitrogen gas, in view of theproductivity. Here, in order to bring the optical constants of the TiNlight absorbing film to a preferred range, it is preferred that thesputtering gas contains nitrogen and a rare gas as main components,wherein the concentration of the nitrogen is from 3 to 50 vol %,preferably from 5 to 20 vol %. If the concentration of the nitrogen isless than this range, the TiN light absorbing film tends to containexcess titanium, whereby the low reflection wavelength region tends tobe narrow. On the other hand, if the concentration of the nitrogen islarger than the range, the TiN light absorbing film tends to containexcessive nitrogen, whereby the low reflection wavelength region tendsto be narrow, and the resistivity of the TiN light absorbing film tendsto be high, whereby the surface resistance tends to be large.

The electric power applied to the target is preferably at a powerdensity of at least 1 W/cm², for the purpose of maintaining the filmforming speed at a level sufficiently quick for industrial productionand maintaining the amount of impurities taken into the TiN film duringthe film formation to a low level. This is particularly effective tocontrol the amount of oxygen to be taken into the film, as describedhereinafter. Further, the electric power applied to the target at thattime is preferably at a power density of at most 10 W/m² in order toobtain a TiN film having proper optical constants and to avoidoccurrence of abnormal discharge or dissolution of the cathode or thetarget by an excess application of the electric power to the target.Namely, if an electric power larger than this is applied, even in anatmosphere of pure N₂, the film will be a TiN film rich in Ti, wherebythe desired composition can hardly be obtained, and the target and itsperipheral parts will be heated, whereby arching or in some casesmelting of the heated parts will be likely to occur.

The presence of a small amount of impurities in the composition of thetarget or the sputtering gas creates no problem so long as it is withina range where the thin film finally formed has substantially the opticalconstant of titanium nitride. Further, the TiN light absorbing film maybe formed by sputtering by using a material consisting essentially oftitanium nitride as the target.

As the TiN light absorbing film, the atomic ratio of nitrogen totitanium in the film is preferably from 0.5 to 1.5 from the viewpoint ofthe optical constants and the resistivity. If the atomic ratio is lessthan 0.5, the product will be a titanium nitride film containing aslightly excess amount of titanium, whereby the optical constant will beimproper, and the antireflection effect tends to be inadequate, althoughthe resistivity can be lowered. On the other hand, if it exceeds 1.5,the product will be a titanium nitride film containing an excess amountof nitrogen, whereby the optical constant changes, and the resistivityincreases, and consequently both the reflectance and the surfaceresistance tend to be unsatisfactory.

Especially from the viewpoint of the antireflection, the atomic ratio ofnitrogen to titanium in the film is preferably from 0.75 to 1.30.

On the other hand, it has been found that by the presence of oxygen,adhesion with the substrate as an oxide or with the silica film as theupper layer will be improved. Accordingly, so long as the opticalconstants of TiN are maintained within a preferred range, in some cases,the presence of oxygen in the. TiN film is preferred.

Further, as a TiN light absorbing film, the atomic ratio of oxygen totitanium in the film is preferably at most 0.5 from the viewpoint of theoptical constant and the resistivity. If this ratio is larger than 0.5,the product will be titanium oxide nitride film, whereby the resistivityincreases, and the optical constant will be improper, and consequentlyboth the surface resistance and the antireflection effect will beunsatisfactory.

In a case where a TiN film is formed by a usual sputtering method, it isunavoidable that oxygen will be contained in the film due to theresidual gas component in the vacuum chamber. The influence of theoxygen in the film over the optical characteristics of a TiN film hasnot heretofore been well known. Especially, nothing has been known aboutan influence over the performance as a light absorbing layer in thepresent invention. The present inventors have conducted extensivestudies on the relation between the film forming conditions for TiN andthe amount of oxygen in the TiN film and the relation with theperformance as a light absorbing layer in the present invention, and asa result, have found that as the TiN light absorbing film in the presentinvention, the atomic ratio of oxygen to titanium in the film ispreferably at most 0.4. If this ratio exceeds 0.4, the dispersionrelation of the optical constants of TiN will be shifted from apreferred range, whereby the low reflection characteristics willdeteriorate. Further, the product will be an oxy-nitride film, wherebythe resistivity will increase, and the surface resistance exceeds 1 kΩ/□which is required for shielding electromagnetic waves, such beingundesirable.

By properly selecting the TIN film-forming method and the film-formingconditions on the basis of the above findings, it is possible to form aTiN film so that the reflectance, when a silica film is formed thereonin an optimum thickness, will not exceed 0.6% in a wide wavelengthregion covering from 500 to 650 nm, as will be shown by the Examplesgiven hereinafter.

As described in the foregoing, in the present invention, it is possibleto obtain a laminate having excellent low reflection characteristicswhen the optical constants of TiN to be used, is maintained within acertain preferred range.

With respect to the optical constant, a more detailed description willbe given as follows.

With a conventional double layer antireflection film employing atransparent film, the reflectance at a designed wavelength can be madecompletely zero by selecting the refractive index and the film thicknessof each layer depending upon the refractive index of the substrate.However, such antireflection conditions will be broken at a wavelengthother than the designed wavelength. Namely, on the longer and shortersides of the designed wavelength, the reflectance sharply increases toform a so-called "V coat", whereby low reflection within a widewavelength range intended by the present invention can not be attained.

On the other hand, when a light absorbing film is employed as aconstituting element, parameters which a single film has, increase fromtwo i.e. (n,d) (n: refractive index, d: geometrical film thickness) ofthe transparent film to three i.e. (n,k,d) (k: extinction coefficient),and with a light absorbing film, the wavelength dependency (dispersion)of (n,k) is substantial, whereby if a light absorbing film having anideal wavelength distribution of (n,k) is formed in a predetermined filmthickness, it is theoretically possible to make the reflectancecompletely zero at every wavelength, when combined with a transparentfilm laminated thereon.

Here, FIG. 16 shows an example of a theoretical calculation conducted bythe present inventors, which shows the distribution relation of (n,k)necessary to bring the reflectance zero over the entire visible lightregion in a case of laminating 15 nm of a light absorbing film as alower layer and 100 nm of SiO₂ as an upper layer. If a material having(n,k) as shown in this Figure is discovered or synthesized, it ispossible to realize a completely antireflection film with a double layerstructure. However, as is apparent from this Figure, such a material cannot be realized, since a wavelength region is present wherein k musthave a negative value.

The present inventors have made a search for a material having opticalconstants close to this ideal (n,k). As a result, it has been found thattitanium nitride, zirconium nitride and hafnium nitride are prospectivecandidates.

Further, the present inventors have conducted various experiments usinga sputtering method and as a result, have found it possible to obtain adouble layer film construction having excellent low reflectioncharacteristics over a wide wavelength range by selecting certainspecific materials, specific film forming conditions or filmthicknesses.

As the silica film to be used for the first and second aspects of theinvention, it is preferred to employ the one formed by DC sputtering ofan electroconductive Si target in the presence of oxygen gas, from theviewpoint of the productivity. Here, to provide electrical conductivityto the target, a small amount of impurities may be mixed. Inclusive ofsuch a case, the silica film here may usually contain a small amount ofimpurities, and even then, it represents a film having substantially thesame refractive index as silica.

In the DC sputtering of Si, arcing is likely to be induced by chargeaccumulation on an insulating silica film deposited along the peripheryof the eroded region of the target, whereby discharge tends to beunstable, and Si or silica particles ejected from the arc spot arelikely to deposit on the substrate to form defects. To prevent suchphenomena, it is common to employ a method of neutralizing the charge byperiodically bringing the cathode to a positive voltage. To use a silicafilm formed by such a method is particularly preferred also from theviewpoint of the stability of the process. As a method for forming thesilica film, RF sputtering may also be employed.

The light absorptive antireflection film of the present inventionexhibits excellent antireflection characteristics. However, thereflectance at the center portion of the visible light region isparticularly low, and the reflection color tends to be blue to purple.If the film thickness of the silica layer becomes thick, the blue tendsto increase. Inversely, if the film thickness of the silica film becomesthin, red tends to increase. Further, as the film thickness of the lightabsorbing film becomes thick, the color becomes deep. Inversely, if thefilm thickness of the light absorbing film becomes thin, the color tendsto be colorless. Accordingly, the film thickness may be adjustedappropriately depending upon the particular purpose.

In the present invention, an additional thin film layer may be formed,as the case requires, for the purpose of improving the adhesion at theinterface or adjusting the color.

Further, an oil repellent organic film containing fluorocarbon may alsobe formed on the outermost layer in order to facilitate wiping off afinger print on the outermost surface. The forming method may, forexample, be a vapor deposition method or a coating and drying method,and in any case, the film is formed to be very thin so that no opticalinfluence will be presented. By applying such treatment, theantireflection film surface will be resistant to soiling, and if soiled,the soil can readily be wiped off.

For the light absorptive antireflection film of the present invention,it is preferred that film forming is carried out by properly adjustingthe film forming conditions and the film thicknesses of the respectivelayers so that the reflectance will not exceed 0.6% in a wide wavelengthregion of from 500 to 650 nm. It is particularly preferred that eachlayer is formed so that the reflectance will not exceed 1.0% within arange of from 450 to 650 nm. More preferably, each layer is formed sothat the reflectance will not exceed 0.6% within a range of from 450 to650 nm.

The light absorptive antireflector of the present invention absorbs apart of incident light to reduce the transmittance. Accordingly, when itis applied to the front glass of a display, the intensity of the lightray which enters from the surface and then is reflected by the surfaceof the display element side, will decrease, whereby the ratio of thedisplay light to this background light is increased to improve thecontrast.

In the present invention, the substrate, the light absorbing film, thetransparent film having a high refractive index and the silica film areso set that the overall reflectance determined by the Fresnel reflectioncoefficients at the respective interfaces, the phase differences betweenthe respective interfaces and the amplitude attenuation degrees withinthe respective layers, will be sufficiently low within the visible lightregion.

Especially, the optical constants of the light absorbing film showdependency which is different from the dispersion relation (wavelengthdependency) of a usual transparent film in the visible light region.Accordingly, by using a light absorbing film material showing a properdispersion relation as the first layer, the low reflection region in thevisible light range can be broadened as compared with the case where thefirst layer is constituted only by a transparent film. This effect isremarkable when a nitride of at least one metal selected from the groupconsisting of titanium, zirconium and hafnium, is used as the lightabsorbing film.

It is not clearly understood why the low reflection characteristics canbe realized over a wide wavelength range as shown by the followingExamples by the film construction of the present invention. This is,however, believed to be attributable to the fact that the opticalconstants of the light absorbing thin film are unexpectedly close to theideal values. The following factors may be mentioned as the causes:

1 The film thickness is thin, whereby the film is not really a uniformfilm, and the optical constants may have a distribution. in thedirection of the thickness or in the direction of the plane, and theymay approach to more ideal values in equivalence.

2 By the specific film forming conditions, a film having the opticalconstants which have not been known (closer to the ideal) has beenobtained.

3 In the process for forming the silica film as the upper layer, theupper portion of the light absorbing film of the lower layer ispartially oxidized, whereby the substantial optical constants havechanged (to more ideal values).

According to the present invention, it is possible to realize a lightabsorptive antireflector having excellent low reflectioncharacteristics, which consists essentially of two layers or threelayers and which has the above-mentioned effects, by forming TiN havingan optical constant within a certain preferred range.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to such specific Examples.

EXAMPLE 1

In a vacuum chamber, metal titanium and N-type silicon (phosphorus dopedsingle crystal) having a resistivity of 1.2 Ω.cm were set as targets ona cathode, and the vacuum chamber was evacuated to 1×10⁻⁵ Torr. A doublelayer film was formed as follows on a soda lime glass substrate 10 setin the vacuum chamber, to obtain a light absorptive antireflector asshown in FIG. 1.

As a discharge gas, a gas mixture comprising argon and nitrogen(nitrogen being 20 vol %) was introduced, and conductance was adjustedso that the pressure become 2×10⁻³ Torr. Then, a negative direct currentvoltage (input power density was about 2.0 W/cm²) was applied to thetitanium cathode, and a titanium nitride film 11 of 14 nm (geometricalfilm thickness, the same applies to film thickness mentionedhereinafter) was formed by DC sputtering of the titanium target (step1).

Then, introduction of the gas was stopped, and the interior of thevacuum chamber was brought to a high level of vacuum. Then, a gasmixture comprising argon and oxygen (oxygen being 50 vol%) wasintroduced as a discharge gas, and conductance was adjusted so that thepressure became 2×10⁻³ Torr. Then, a voltage with a waveform as shown inFIG. 3 was applied to the silicon cathode, and a silica film 13 having arefractive index of 1.46 of 100 nm was formed by intermittent DCsputtering of the silicon target (step 2).

The spectral transmittance of the obtained light absorptiveantireflection glass was measured. Further, the spectral reflectance ofthis sample was measured from the film surface side in such a state thata black lacquer was coated on the rear side of the glass substrate toeliminate the reflection on the rear side. FIG. 4 shows curve 42 of thespectral transmittance and curve 41 of the spectral reflectance, thusobtained.

Further, after step 1, the titanium nitride film-deposited glasssubstrate was taken out, and the titanium nitride film was analyzed byESCA, whereby the atomic ratio was Ti:N:O=1:0.86:0.16.

EXAMPLE 2

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A double layer film was formed asfollows on a soda lime glass substrate set in the vacuum chamber.

A titanium nitride film of 14 nm was formed in the same manner as inExample 1 except that in step 1 of Example 1, the discharge gas waschanged to nitrogen gas (100% nitrogen).

Then, in the same manner as in step 2 of Example 1, a silica film of 100nm was formed.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.92:0.20.

EXAMPLE 3

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A double layer film was formed asfollows on a soda lime glass substrate set in the vacuum chamber.

A titanium nitride film of 12 nm was formed in the same manner as inExample 1 except that in step 1 of Example 1, the discharge gas waschanged to 10% nitrogen gas.

Then, in the same manner as in step 2 of Example 1, a silica film of 85nm was formed.

With respect to the obtained light absorptive antireflection glass,curve 61 of the spectral reflectance was measured in the same manner asin Example 1. The results are shown in FIG. 6.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.95:0.08.

Further, with respect to the obtained light absorptive antireflectionglass, heat treatment at 450° C. for 30 minutes was applied three times,and the curve of the spectral reflectance after the heat treatment isshown in FIG. 14.

EXAMPLE 4

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A double layer film was formed asfollows on a soda lime glass substrate set in the vacuum chamber.

In the same manner as in Example 3, a titanium nitride film of 7 nm, anda silica film of 85 nm were formed.

With respect to the obtained light absorptive antireflection glass, thecurve of the spectral reflectance was measured in the same manner as inExample 1. The results are shown in FIG. 10.

After forming the titanium nitride film, the substrate was taken out inthe same manner as in Example 1, and the titanium nitride film wasanalyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.95:0.09.

EXAMPLE 5

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁵ Torr. A double layer film was formed asfollows on a soda lime glass substrate set in the vacuum chamber.

In the same manner as in step 1 of Example 1, a titanium nitride film of20 nm was formed.

Then, in the same manner as in step 2 of Example 1, a silica film of 100nm was formed.

With respect to the obtained light absorptive antireflection glass, thecurve of the spectral reflectance was measured in the same manner as inExample 1. The results are shown in FIG. 11.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.84:0.17.

EXAMPLE 6

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A multilayer film was formed asfollows on a soda lime glass substrate set in the vacuum chamber.

In the same manner as in step 1 of Example 1, a titanium nitride film of14 nm was formed.

Then, the discharge gas was changed to 100% argon, and the pressure wasadjusted to 2×10⁻³ Torr. Then, a negative direct current voltage wasapplied to the silicon cathode, and a silicon film of 2 nm was formed asan oxidation barrier layer by DC sputtering of the silicon target.

Then, in the same manner as in step 2 of Example 1, a silica film of 100nm was formed.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.88:0.14.

EXAMPLE 7

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A multilayer film was formed asfollows on a soda lime glass substrate set in the vacuum chamber.

Firstly, in the same manner as in Example 3, a titanium nitride film of12 nm was formed. Then, the discharge gas was changed to 30% nitrogen,and the pressure was adjusted to 2×10⁻³ Torr. Then, a negative directcurrent voltage was applied to the silicon cathode, and a lightabsorptive silicon nitride film of 5 nm was formed as an oxidationbarrier layer by DC sputtering of the silicon target.

Then, in the same manner as in Example 3, a silica film of 85 nm wasformed thereon.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.97:0.06.

Further, with respect to the obtained light absorptive antireflectionglass, heat treatment at 450° C. for 30 minutes was applied three times,and the curve of the spectral reflectance after the heat treatment isshown in FIG. 15.

EXAMPLE 8

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. Oxygen gas introduced as adischarge gas, and the pressure was adjusted to 2×10⁻³ Torr. Then, anegative direct current voltage was applied to the titanium cathode, anda titanium oxide film of 3 nm was formed as an under layer on a sodalime glass substrate set in the vacuum chamber by DC sputtering of thetitanium target.

Then, in the same manner as in Example 3, a titanium nitride film of 12nm and a silica film of 85 nm were formed on the titanium oxide film.

With respect to the obtained light absorptive antireflection glass,curve 71 of the spectral reflectance was measured in the same manner asin Example 1. The results are shown in FIG. 7.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.93:0.07.

EXAMPLE 9

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A double layer film was formed asfollows on a PET substrate (provided with a hard coat, 150 μm thick) setin the vacuum chamber.

In the same manner as in Example 3, a titanium nitride film of 12 nm anda silica film of 85 nm were formed.

The obtained PET provided with a light absorptive antireflection film,curve 81 of the spectral reflectance was measured in the same manner asin Example 1. The results are shown in FIG. 8.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.91:0.11.

EXAMPLE 10

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A three layer film was formed asfollows on a soda lime glass substrate 20 set in the vacuum chamber toobtain a light absorptive antireflector as shown in FIG. 2.

Using the same gas and pressure as used in step 1 of Example 1, anegative direct current voltage was applied to the titanium cathode, anda titanium nitride film 21 of 30 nm was formed by DC sputtering of thetitanium target.

Then, introduction of the gas was stopped, and the vacuum chamber wasbrought to a high level of vacuum. Then, using the same gas and pressureas used in step 1 of Example 1, a negative direct current voltage wasapplied to the titanium cathode, and a titanium oxide film 22 of 18 nm(refractive index: about 2.2) was formed by DC sputtering of thetitanium target.

Then, while maintaining the introduction of the gas, a voltage of thewaveform as shown in FIG. 3 was applied to the silicon cathode, and asilica film 23 of 63 nm was formed by intermittent DC sputtering of thesilicon target.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.87:0.14.

EXAMPLE 11

A light absorptive antireflector provided with a three layer film wasobtained in the same manner as in Example 10 except that the targets inExample 10 were changed to metal titanium, ITO (tin-doped indium oxide)and N-type silicon (phosphorus-doped single crystal) having aresistivity of 1.2 Ω.cm to form an ITO film (refractive index: about2.0) instead of the titanium oxide film in Example 10, and the filmthicknesses of the titanium nitride film and the silica film werechanged.

Namely, in the same manner as in Example 10, firstly a titanium nitridefilm of 23 nm was formed, and then using an ITO cathode instead of thetitanium cathode of Example 10, DC sputtering was carried out in thesame manner except that a gas mixture of argon and oxygen (oxygen being1 vol %) was used as the discharge gas, to form an ITO film of 22 nm.Finally, a silica film of 59 nm was formed.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.86:0.18.

EXAMPLE 12

Using the same apparatus and targets as used in Example 10, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. Oxygen was introduced as adischarge gas, and the pressure was adjusted to 2×10⁻³ Torr. Then, anegative direct current voltage was applied to the titanium cathode, anda titanium oxide film of 3 nm was formed as an under layer on a sodalime glass substrate set in the vacuum chamber by DC sputtering of thetitanium target.

Then, in the same manner as in Example 10, a titanium nitride film of 30nm, a titanium oxide film of 18 nm and a silica film of 63 nm weresequentially formed on the titanium oxide film of 3 nm.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.85:0.17.

EXAMPLE 13

Using the same apparatus and targets as used in Example 10, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A three layer film was formed asfollows on a soda lime glass substrate set in the vacuum chamber.Firstly, in the same manner as in Example 10, a titanium nitride film of30 nm was formed. Then, the discharge gas was changed to 100% of argon,and the pressure was adjusted to 2×10⁻³ Torr. Then, a negative directcurrent voltage was applied to the silicon cathode, and a silicon filmof 3 nm was formed as an oxidation barrier layer by DC sputtering of thesilicon target.

Then, in the same manner as in Example 10, a titanium oxide film of 18nm and a silica film of 63 nm were formed thereon.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.88:0.16.

EXAMPLE 14

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A double layer film comprising 9nm of a titanium nitride film and 85 nm of a silica film, was formed ona soda lime silica glass substrate set in the vacuum chamber in the samemanner as in Example 3.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.94:0.11.

The spectral reflectance of the obtained sample was measured in the samemanner as in Example 1. The results are shown in FIG. 12.

EXAMPLE 15

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A double layer film was formed asfollows on a soda lime silica glass substrate set in the vacuum chamber.

Firstly, in the same manner as in Example 3, a titanium nitride film of12 nm was formed in a 10% nitrogen atmosphere. At that time, theelectric power applied to the titanium target was adjusted to 1/4 of thepower in Example 3. The power density applied here was about 0.5 W/cm².Then, in the same manner as in Example 3, a silica film of 102 nm wasformed.

After formation of the titanium nitride film, the substrate was takenout in the same manner as in Example 1, and the titanium nitride filmwas analyzed by ESCA, whereby the atomic ratio was Ti:N:O=1:0.70:0.65.

The spectral reflectance of the obtained sample was measured in the samemanner as in Example 1. The results are shown in FIG. 13.

EXAMPLE 16 (COMPARATIVE EXAMPLE)

A double layer film-attached antireflector was prepared in the samemanner as in Example 1 except that the targets in Example 1 were changedto ITO (tin-doped indium oxide) and N-type silicon (phosphorus-dopedsingle crystal) having a resistivity of 1.2 Ω.cm to form an ITO filminstead of the titanium nitride film in Example 1, and the thickness ofthe silica film was changed.

Namely, DC sputtering was carried out in the same manner as in Example 1except that an ITO cathode was used instead of the titanium cathode inExample 1, and a gas mixture of argon and oxygen (oxygen being 1 vol %)was used as a discharge gas, to form an ITO film of 30 nm, and then asilica film of 110 nm was formed in the same manner as in Example 1.

With respect to the obtained sample, the curve 52 of spectraltransmittance and the curve 51 of the spectral reflectance were measuredin the same manner as in Example 1. The results are shown in FIG. 5.

EXAMPLE 17 (COMPARATIVE EXAMPLE)

Using the same apparatus and targets as used in Example 1, the vacuumchamber was evacuated to 1×10⁻⁵ Torr. A double layer film was formed asfollows on a soda lime glass substrate set in the vacuum chamber.

In the same manner as in Example 1, a titanium nitride film of 30 nm anda silica film of 100 nm were formed.

With respect to the obtained sample, the curve 92 of spectraltransmittance and the curve 91 of spectral reflectance were measured inthe same manner as in Example 1. The results are shown in FIG. 9.

Further, after formation of the titanium nitride film, the substrate wastaken out in the same manner as in Example 1, and the titanium nitridefilm was analyzed by ESCA, whereby the atomic ratio wasTi:N:O=1:0.87:0.15.

A square sample of 3×3 cm was cut out from each of the antireflectionglasses obtained in the above Examples 1 to 17, and electrodes wereformed at the four corners of the film surface by glass solder. Thesurface resistance as measured by a Van der Paun method, the visualreflectance and the visual transmittance obtained from the spectralcurve, and the light absorption to incident light from the silica filmside (hereinafter refereed to simply as a light absorption) aresummarized in Table 1.

To the same light absorptive antireflection glass, heat treatment at450° C. for 30 minutes was applied three times, whereupon the surfaceresistance, the visual reflectance, the visual transmittance, the lightabsorption as measured in the same manner and the wavelength range wherethe reflectance is at most 0.6%, are shown in Table 1. In Table 1,"before" and "after" mean before the heat treatment and after the heattreatment, respectively.

As is evident from Table 1 and FIGS. 4 to 15, according to the presentinvention, a light absorptive antireflection glass excellent in heatresistance can be realized with a simple film construction.

When the spectral reflectance curve of Example 1 is compared withExample 16 (Comparative Example) constituted by a transparent film only,it is evident that with the spectral reflectance curve of Example 1, thelow reflection region is wide, thus indicating excellent antireflectioncharacteristics.

Further, as is evident from the spectral transmittance curve and thevisual transmittance in Table 1, the light absorbing film employed inthe present invention is capable of reducing the transmittance ascompared with a transparent antireflection film. Accordingly, when thepresent invention is applied to a panel glass a face plate or a filterglass, set in front of the display screen of e.g. CRT, the effect forimproving the contrast of the display screen is remarkable as comparedwith a transparent antireflection film.

Further, as is evident from these Examples, according to the presentinvention, the light absorption to incident light from the silica filmside of the light absorptive antireflection film of the presentinvention can be adjusted within a range of from 10 to 35% by selectingthe film thickness of the light absorbing film within a preferred range.Of course, as is evident from the graph of the spectral reflectance inExamples, if the thickness of the light absorbing film is increased, thelow reflection wavelength region becomes narrow. Accordingly, the filmthickness may be selected depending upon the particular purpose.

Further, as is evident from comparison between Examples 1 to 5 and 14,FIG. 4, FIG. 6, FIG. 10 and FIG. 11, and Examples 17 (ComparativeExample) and FIG. 9, it is possible to make the antireflectionperformance excellent by properly selecting the film forming conditionsand the film thickness for titanium nitride and the film thickness ofthe silica film. However if titanium nitride is formed in a thinthickness to improve the antireflection performance, the heat resistancetends to be slightly low, and the property change after the heattreatment tends to be slightly large.

As is evident from Example 5, if the film thickness of titanium nitrideis made thick, the change in the properties by heat treatment will bereduced as compared with the case where the film is thin. However, insuch a case, the visual reflectance before the heat treatment is as lowas 0.12%, but an increase in the reflectance is remarkable at the bothends of the wavelength region of the visible light, and the reflectioncolor is light blue purple.

As is evident from Examples 6 and 7, even if the film thickness oftitanium nitride is made thin, the heat resistance can remarkably beimproved by forming an oxide barrier layer on the titanium nitride film.

As is evident from Example 8 and FIG. 7, the reflection color can bemade close to colorless by inserting a reflection color-adjusting layerin the film construction.

As is evident from Example 9 and FIG. 8, a light absorptiveantireflector showing excellent low reflection characteristics can beobtained by the present invention, even when a plastic material isemployed as the substrate.

Further, the samples of Examples 1 to 15 were subjected to scratchresistance tests by erasers (load: 500 g, 20 reciprocations) before andafter the heat treatment. As a result, any scratch mark which will bepractically problematic, was not observed in each case. Especially inExamples 1 to 9, 14 and 15, no scratch mark was observed.

                                      TABLE 1                                     __________________________________________________________________________         Surface                                                                             Visual                                                                              Visual                                                                              Light Wavelength range (nm)                                 resistance                                                                          resistance                                                                          transmittance                                                                       absorptivity                                                                        wherein the reflectance                               (kΩ/□)                                                             (%)   (%)   (%)   is at most 0.6%                                  Example                                                                            Before/after                                                                        Before/after                                                                        Before/after                                                                        Before/after                                                                        Before/after                                     __________________________________________________________________________     1   0.63/1.45                                                                           0.10/0.08                                                                           69.3/72.1                                                                           28.4/25.4                                                                           472-746/467-744                                   2   2.33/6.52                                                                           0.18/0.23                                                                           62.7/66.8                                                                           35.3/30.9                                                                           496-677/489-680                                   3   0.35/1.84                                                                           0.08/0.38                                                                           66.3/70.2                                                                           31.6/27.2                                                                           428-721/415-601                                   4   0.87/7.55                                                                           0.24/1.87                                                                           75.8/81.0                                                                           21.3/14.1                                                                           404-660/412-481                                   5   0.40/0.85                                                                           0.12/0.11                                                                           60.1/63.3                                                                           38.1/33.8                                                                           485-654/471-655                                   6   0.61/0.71                                                                           0.11/0.10                                                                           66.2/69.1                                                                           31.7/28.6                                                                           475-736/461-738                                   7   0.39/0.33                                                                           0.10/0.11                                                                           68.7/70.6                                                                           29.0/27.0                                                                           427-719/420-744                                   8   0.35/1.69                                                                           0.35/0.39                                                                           65.9/70.3                                                                           31.8/27.1                                                                           438-667/435-661                                   9   0.87/--                                                                             0.33/--                                                                             65.4/--                                                                             32.3/--                                                                             455-681/--                                       10   0.25/0.66                                                                           0.12/0.09                                                                           49.6/52.3                                                                           49.2/46.4                                                                           422-734/418-745                                  11   0.18/0.23                                                                           0.15/0.12                                                                           58.5/61.7                                                                           39.8/36.4                                                                           416-723/419-732                                  12   0.26/0.71                                                                           0.37/0.33                                                                           48.9/53.0                                                                           49.6/45.4                                                                           424-709/417-713                                  13   0.23/0.31                                                                           0.14/0.12                                                                           45.4/48.5                                                                           53.5/50.3                                                                           418-717/414-715                                  14   0.65/4.81                                                                           0.15/0.64                                                                           71.3/75.6                                                                           26.3/21.2                                                                           419-693/412-689                                  15   1.12/8.71                                                                           0.74/1.84                                                                           71.9/76.9                                                                           25.0/18.6                                                                           501-595/--                                       16   0.22/0.47                                                                           0.82/0.57                                                                           94.7/95.0                                                                            0.4/0.3                                                                            532-625/514-612                                  17   0.22/0.29                                                                           1.22-1.13                                                                           48.7/50.9                                                                           49.0/46.8                                                                           --/--                                            __________________________________________________________________________

The multilayer film to be used for the light absorptive antireflector ofthe present invention, has a proper light absorption and antireflectionperformance, and can be realized in a simple film construction andwithout increasing the total film thickness.

Further, by reducing the transmittance, it is possible to increase thecontrast. With a surface resistance being at most 1 kΩ/□, it is possibleto obtain a light absorptive antireflector having an electromagneticwave-shielding effect.

Further, the present invention takes substantially a double layer orthree layer construction, whereby as compared with a conventionalantireflection film having a multilayer construction, the number ofinterfaces is small, and it is excellent in the heat resistance and themechanical strength such as scratch resistance. This is remarkableespecially in the case of a double layer construction according to thefirst aspect of the invention.

Further, when DC sputtering is used for a film forming method in thepresent invention, there will be a merit in that the stability of theprocess is assured, and a film with a large area can readily be formed.In addition to such features, a light absorptive antireflector can beproduced at a low cost.

Further, the light absorptive antireflector according to the presentinvention, is excellent in the heat resistance and sufficiently durableagainst heat treatment at a level required for the panel glass of acathode ray tube. Such a construction is expected to be useful for otherapplications where the heat resistance is required.

What is claimed is:
 1. A light absorptive antireflector comprising asubstrate, a single light absorbing film, wherein the light absorbingfilm is formed on the substrate, and a silica film formed on the lightabsorbing film, to reduce reflection of incident light from the silicafilm side,wherein the light absorbing film is a film consistingessentially of a nitride of titanium, and the film consistingessentially of a nitride of titanium, is a film containing oxygen in anamount of from about 0.06 to at most 0.5 as an atomic ratio to titanium,wherein the geometrical film thickness of the light absorbing film isfrom 5 to 25 nm, and the geometrical film thickness of the silica filmis from 70 to 110 nm.
 2. The light absorptive antireflector according toclaim 1, wherein the geometrical film thickness of the light absorbingfilm is from 7 to 20 nm.
 3. The light absorptive antireflector accordingto claim 1, wherein the geometrical film thickness of the lightabsorbing film is from 10 to 20 nm.
 4. The light absorptiveantireflector according to claim 1, wherein the geometrical filmthickness of the light absorbing film is from 7 to 15 nm.
 5. The lightabsorptive antireflector according to claim 1, wherein the geometricalfilm thickness of the silica film is from 80 to 100 nm.
 6. The lightabsorptive antireflector according to claim 1, wherein the lightabsorption of the light absorptive antireflector is from 10 to 35% tothe incident light from the silica film side.
 7. The light absorptiveantireflector according to claim 1, wherein the reflectance of the lightabsorptive antireflector to the incident light from the silica film sidedoes not exceed 0.6% in a wavelength region of from 500 to 650 nm. 8.The light absorptive antireflector according to claim 1, wherein a layerconsisting essentially of a metal or metal nitride and having ageometrical film thickness of from 1 to 20 nm, is formed between thelight absorbing film and the silica film.
 9. The light absorptiveantireflector according to claim 8, wherein the layer consistingessentially of the metal or metal nitride, is a layer consistingessentially of silicon or silicon nitride.
 10. The light absorptiveantireflector according to claim 1, wherein the substrate is a glasssubstrate, a plastic substrate or a plastic film, which constitutes thefront surface of a display screen.
 11. The light absorptiveantireflector according to claim 1, wherein the substrate is a panelglass, constituting a cathode ray tube.
 12. The light absorptiveantireflector according to claim 1, wherein the reflectance of the lightabsorptive antireflector to the incident light from the silica film sideafter heating does not exceed 0.6% in a wavelength region of from 500 to650 nm.
 13. A method of producing a cathode ray tube with a lightabsorptive antireflector, comprising forming a light absorbing film on apanel glass for a cathode ray tube, forming a silica film on the lightabsorbing film, and heating the panel glass to obtain a cathode raytube, wherein the light absorbing film is a film consisting essentiallyof a nitride of titanium, and the film consisting essentially of anitride of titanium, is a film containing oxygen in an amount of at most0.5 as an atomic ratio to titanium.